The present invention relates generally to machines that employ reciprocating blades for cutting sheet-type work materials, and deals more particularly with an apparatus for performing a dual sharpening operation on the cutting edge of the blade, whereby a primary sharpener is used to sharpen the entire cutting edge of the blade, and a secondary sharpener is utilized between primary sharpening operations to sharpen only a portion of the cutting edge that initially becomes dull.
Reciprocating blades are used to cut sheet type work materials in a variety of high-speed, large-volume cutting operations. For example, such blades are employed in reciprocating blade cutting heads used on cloth cutting machines where pattern pieces are simultaneously cut from one to several sheets of fabric stacked one-on-top-of-the-other. Due to the high throughput rates of this type of cutting machinery, the cutting edge of the blade becomes dull and requires sharpening at regular intervals.
In addition to the cutting edge becoming dull, another difficulty that sometimes occurs in high-speed, large-volume cutting machinery is that the geometry of the leading edge portion of the cutting edge becomes displaced relative to the remainder of the cutting edge. This is especially problematic in machinery where closed complex shapes are cut requiring the blade to turn in the same cutting direction in order to follow the outline of the closed piece shape. This overall net unidirectional change imparts a significant lateral load on the cutting edge of the blade causing a concomitant distortion in geometry, a phenomena referred to as xe2x80x9cedge rollover.xe2x80x9d This loss of geometric integrity causes further degradation of the blade""s cutting edge to occur at an accelerated rate such that a complete sharpening of the entire cutting edge is required at an interval considerably shorter than that which would occur simply as a result of dulling. Each time the cutting edge is completely sharpened a significant amount of material is removed from the blade, causing a concomitant reduction in the blade""s useful life. In addition, the time spent sharpening reduces throughput of the machine.
Based on the foregoing, it is the general object of the present invention to provide an apparatus for sharpening or reforming the cutting edge of a blade used in reciprocating blade cutting machines that overcomes the above-described drawbacks of prior sharpening devices.
It is a more specific object of the present invention to provide an apparatus for prolonging the period between which the entire surface of the cutting edge of a reciprocating blade used in cutting machines must be sharpened.
The present invention is directed to a sheet material cutting apparatus including a frame having a work supporting surface for carrying sheet-type work materials, such as one or more layers of fabric stacked one-on-top-of-the-other. The apparatus also includes a cutting head coupled to the frame adjacent to the work supporting surface. The cutting head includes a knife frame rotatably mounted thereon for rotation relative to the frame. An elongated blade is coupled for reciprocation to the knife frame and includes cutting surfaces that together define a cutting edge. The blade is movable between a lowered position, whereby the blade can engage the work material, and a raised position whereby the blade is located above the work material. Drive means are also associated with the cutting head for rotating the knife frame about an axis perpendicular to the work supporting surface to orient the cutting edge of the blade in a particular cutting direction. A primary sharpener is coupled to the knife frame and can be selectively engaged with at least one of the cutting surfaces while the blade reciprocates, thereby sharpening the blade by removing material along substantially the entire cutting edge.
A secondary sharpener, for maintaining the sharpness of the cutting edge of the blade between primary sharpening operations is also provided. The secondary sharpener is coupled to a presser foot, which in turn is coupled to the knife frame. The presser foot is moveable between a lowered working position where it engages and exerts pressure on the sheet-type work material, and a raised non-working position whereby the presser foot is located above the work material. Between primary sharpening operations, with the presser foot in the non-working position, and the blade in the raised position, the secondary sharpener can be selectively engaged with a portion of at least one of the cutting surfaces of the blade to sharpen only that portion of the blade where degradation of the cutting edge generally initiates. Use of the secondary sharpener prolongs the life of the blade by extending the time between primary sharpening operations thereby minimizing the amount of material which must be removed from the blade""s cutting edge to maintain sharpness. While the secondary sharpener is described above as being coupled to the presser foot, the present invention is not limited in this regard as the secondary sharpener can be mounted to the cutter head or frame without departing from the broader aspects of the present invention.
In a preferred embodiment of the present invention, the primary sharpener includes at least one abrasive grinding wheel coupled to the knife frame adjacent to the cutting edge of the blade. The grinding wheel can be selectively engaged with at least one of the cutting surfaces to remove material from the surface and thereby sharpen the blade. The secondary sharpener preferably includes a sharpening member slidably coupled to at least one guide-rail which in turn is coupled to the presser foot adjacent to the cutting edge of the blade. Biasing means mounted on the guide rail are interposed between the presser foot and the sharpening member to urge the sharpening member away from the cutting edge during a cutting operation. In addition, means for causing the secondary sharpener to selectively engage a portion of at least one of the cutting surfaces of the blade in response to commands issued from a controller are also included.
In one embodiment, the means for causing the secondary sharpener to selectively engage at least one of the cutting surfaces includes an actuating arm extending from the knife frame and having a tapered surface positioned adjacent to the sharpening member. As the presser foot is moved from the working to the non-working position, and the blade is moved to the raised position, the actuating arm progressively engages the sharpening member, urging it into contact with a portion of the cutting edge of the blade. As the blade is reciprocated, material is removed from the portion of the cutting edge by the sharpening member thereby sharpening the blade.
In another embodiment of the present invention, the means for causing the secondary sharpener to selectively engage the cutting edge of the blade includes an actuator, preferably in the form of a solenoid, a pneumatic cylinder, or a hydraulic cylinder coupled to the presser foot and in communication with the sharpening member. The actuator moves the sharpening member into engagement with a portion of the blade""s cutting edge, in response to commands issued from the controller.
In yet a further embodiment of the present invention, the secondary sharpener is slidably positioned on the guide rail; biasing means, preferably in the form of a spring are interposed between the presser foot and the sharpening member for urging the sharpening member away from the blade during a cutting operation. The secondary sharpening operation is performed by moving the presser foot to the non-working position, and the blade to the raised position and then rotating the knife frame at a rate adequate to impart centrifugal force to the sharpening member of a magnitude sufficient to overcome the force exerted on the member by the spring. This in turn causes the sharpening member to engage and sharpen a portion of the cutting edge of the blade during reciprocation.
In yet a further embodiment of the present invention, at least one swing arm is pivotally coupled to the presser foot and the sharpening member. During a cutting operation, biasing means interposed between the swing arm and the presser foot, urge the sharpening member away from the blade""s cutting edge. To perform a secondary sharpening operation, the presser foot is moved to the non-working position, the blade is raised, and the knife frame is rotated such that centrifugal force, adequate to overcome the force exerted against the swing arm by the biasing means, is imparted to the sharpening member causing the sharpening member to engage and sharpen a portion of at least one of the cutting surfaces of the reciprocating blade.
The sharpening member of the secondary sharpener can also include first and second blade shaping surfaces selectively engageable with opposing cutting surfaces which together define the cutting edge of the blade. Rotation of the knife frame in a first rotational direction imparts centrifugal force to the sharpening member causing the swing arm to pivot and the first blade shaping surface to engage a portion of one of the edge surfaces defined by the blade. Rotation of the knife frame in a second rotational direction, opposite to the first rotational direction, causes the second blade shaping surface to engage a portion of an opposite edge surface defined by the blade, thereby sharpening a portion of the cutting edge.